The background of the invention is in problems associated with undesirable pressure build-up especially in annuli, but also in well pipes, in underground wells. This pressure build-up results from associated pressure barrier failures in such wells. Typically, such pressure barriers consist of cement, well liquids, packers, plugs and casings. The purpose of such pressure barriers is to prevent undesirable leakage and flow of well fluids to the surface, but also to/from permeable formations communicating with a well.
Pressure barrier failure may arise in any phase of the lifetime of a well and, depending on the type of well and well phase, such a failure may cause various unfortunate and possibly disastrous consequences. Thus, pressure barrier failure constitutes a problem both in new and old wells, including old wells that have been plugged and abandoned.
Pressure build-up and possible fluid leakages in annuli may arise due to poorly executed cementing jobs. Fluid-conveying channels may also be formed in the cement in the annulus due to setting-related and/or earthquake-related movements in one or more formations surrounding a well. Such setting-related and/or earthquake-related movements may also damage packers, plugs and other well pressure counteracting equipment in a well and thus result in pressure build-up and possible fluid leakages in the well.
Salt water and/or other corrosive fluids in a well may also disintegrate casings, packers plugs and similar in the well and eventually cause pressure build-up and possible fluid leakages in the well.
Incidentally, a well pressure counteracting liquid, for example drilling mud containing weighting materials for increasing the density of the liquid, and which is positioned in an annulus/well pipe for some considerable time, may eventually segregate and deposit its weighting material. Thereby, the majority of the liquid will assume a smaller density and hence will lose its well pressure counteracting effect. This may then cause pressure build-up and possible fluid leakages in the well.
For a production well, pressure barrier failure may lead to shut-down of the production from the well. Pressure barrier failure may also result in undesirable fluid leakage to other permeable formations in the underground. Thus, a leakage in an oil well may cause oil to flow to a groundwater-permeable formation penetrated by the well so as to contaminate the water in the groundwater-permeable formation.
For a plugged and abandoned well, such pressure barrier failure may result in undesirable flow of well fluids to the surface and/or to one or more formations penetrated by the well. Also this may unfortunate and possibly disastrous consequences, for example extensive pollution and related environmental problems.
In this context, comprehensive and international statistics exist over wells encumbered with problems related to such pressure barrier failure. These problems may have large consequences with respect to operations, time, cost, safety and the environment.